Objectives: The unique physicochemical properties of nanoscale (<100 nm) materials results in the potential to revolutionize the electronic, diagnostic, and therapeutic fields. Although some manufactured NPs have been in use for some time, new nanomaterials are rapidly being developed. Existing studies on the effects of ambient air and manufactured nanosized particles have shown that they are more toxic than larger ones and that the observed toxicity is oxidative stress-related. One unique feature of nanosized materials is that the surface area and, therefore the number of reactive molecules at the particle surface, increases as particle size decreases. We hypothesize that the oxidative stress in cells and tissues that has been shown to occur in response to NP is a function of the physicochemical characteristics of the NP surface. To test this hypothesis, we have designed five specific aims to 1) evaluate NP deposition in specific regions of the respiratory tract, translocation, and effects in vivo;2) assess NP interactions with proteins from tissue and cellular extracts;3) evaluate NP uptake and mechanistic aspects of cellular responses;4) fully characterize the physicochemical properties of the NP used for exposures and correlate these characteristics with tissue and cellular responses;and 5) correlate physicochemical NP characteristics with in vivo and in vitro responses. Approach: The hypothesis will be tested using an approach that focuses on the in vivo disposition of and responses to NP. Acellular analyses will assess reactive oxygen species-generating capacity and protein binding. NP uptake and mechanisms of toxicity will be tested in the planned in vitro studies using conventional liquid-phase as well as electrospray aerosol exposures. In vivo studies in rats will focus on inflammation and oxidative stress as well as tissue distribution following respiratory tract exposures. These studies will be accompanied by a thorough physicochemical characterization of the particles used. The final goal will be the development of a much-needed predictive model using correlation statistics that will link NP physicochemical characteristics with outcome measures from the acellular, cellular, and in vivo systems and will also identify the best dose and response metrics. Expected Results: The outcomes of this project that are relevant to public health include determinations of the condition under which NPs move out of the lungs after they are inhaled, if and how they cause tissue and cellular injury, and which people might be the most sensitive to these effects. This information can then be used to predict outcomes of human exposures in various settings and lead to interventions that can protect public health if NPs are found to be injurious.